Choose Your Weapon
Once you've hit 80, as a 2-handed weapon wielder, there's 3 major weapons you want to start shooting for. Here's a look at those three choices and the pros and cons.
The Titansteel Destroyer is a blacksmithed weapon which is a very popular target for new 80 Death Knights, and with good reason. Hard hitting and relatively slow, it's perfect for getting the most damage out your weapon strikes. Plus, the strength, stamina, and hit rating are all incredibly nice for a Death Knight whether you're a tank or a DPSer. Just be prepared to drop around 2-3k gold worth of mats to make it. Also, before someone says something: Yes, it is a mace, but yes, Death Knights can train maces, and it shouldn't take you too long to up your 2-handed Mace skill from 1. I used a Stratholme run to get my 2-handed mace skill up, and the Deathcharger's Reins dropped as a nice bonus
The Colossal Skull-Clad Cleaver is an axe which drops off Loken in Heroic Halls of Lightning, and if you don't have the patience or money to get the mats for the Titansteel Destroyer, it's a pretty decent replacement, with the exact same DPS, weapon speed, and damage range. The one major problem here comes with the stats on the weapon, which include the less useful haste and agility stats. Still, if you're tanking, that agility may actually push the Skull-Clad Cleaver over the Destroyer because of the extra avoidance, and this sword will definitely be cheaper than the Titansteel Destroyer, whatever else.
The Sword of Justice, which drops from the Tribunal Chest at the end of Heroic Halls of Stone, is the dark horse of level 80 Death Knight weapons. It has lower DPS than the other two options by a considerable margin, but it does have a higher top end damage, making weapon strikes hit harder and arguably making it more comparable to the above weapons than one might first think. The stats on it are nice as well, featuring plenty of strength, stamina, and critical strike rating, plus a red gem socket for further customization. Finally, it's a sword, which is nice for Death Knight purists and humans.
Grab Defense Trinkets
If Loken won't drop your Seal of the Pantheon, there's a couple other quick and dirty ways to get defense on a trinket. We've mentioned them before, but it's worth getting into them a little deeper. There's two defense trinkets you might consider picking up in Outland.
The easier one is the Dabiri's Enigma from Netherstorm. You'll want to head the Protectorate Outpost to the Northwest of Manaforge Ultris and talk to, who else, Professor Dabiri. He'll give you a quest that will involve killing the shadow elementals and voidwalkers up at the Manaforge, followed by a quick ride on a Netherdrake to bomb the forge. Both are relatively easy, and will open the quest to kill Dimensius. Dimensius himself still hits pretty hard, so if you're having trouble, hang back and let the Ethereals tank him while you throw out Icy Touches, Blood Boils, and Death Coils. You'll then be able to pick up your reward, which has a useless right click, but does have sweet, sweet defense rating.
For the other, slightly more useful trinket, you'll have to head into Shadow Labyrinth in Auchindoun in Terokkar Forest and kill the second boss, Blackheart the Inciter. This can be done solo, but does take some work. First, you'll need the key to open the door to the instance area. If you didn't have a chance to run Sethekk Halls while leveling up, don't worry, you can probably solo it now. If you sneak through the instance well, you should be able to avoid most of the mobs. You'll still have to fight the guards and ravenguards and the patrolling serpents and non-elite birds, and the group of mobs before Talon-King Ikiss (kill the Prophet first, he fears), though, but all of those should be little problem for you. Even Ikiss will be a cinch, though I'd still hide behind a pillar when he starts casting his Arcane Explosion. Once he's down, loot the chest behind him for the key.
Now that you have the key, you should be able to sneak up to Blackheart's room relatively easily. By sticking to the right wall, you should only have to kill one group in the corner, and you shouldn't have to kill any of the groups around the pillar in the first boss' room. It's when you get to Blackheart's room that it gets tough. You have to kill every single mob in here, or they'll aggro during his fight. Getting the groups down is a bit of a tough job. You'll want to focus on the healers first, of course, though the Shadow Priest mobs hit hard enough to make a dent even in your 80 self, and aren't to be discounted.
It may take you a few deaths to get the hang of clearing this room, but the goods news is that Blackheart himself should be pretty much a pushover when it's time to take him on. If you have a permapet ghoul, he does do his Incite Chaos move, but it doesn't reset his health, so no worries about that. Once you kill him, pray he drops the Adamantine Figurine. If he does, you have a nice defense trinket that even has a usable right click.
Of course, we're getting a lot of nice defense help next patch, so if you want to sit tight and wait for 3.0.8 to come out for your extra defense needs, that's probably cool too.
Choose your faction to grind
So if you read our DK faction gear guide a while back, you probably have a good idea of where you're going with this, but we can review real quick.
If you're a tank, your main goal should probably be to get to Revered with the Wyrmrest Accord and the Argent Crusade as quickly as you can. as they both have some solid tank gear at honored and revered. The Argent Dawn has more quests and dailies available in Zul'drak and Icecrown, so you'll probably focus on questing for the Argent Dawn, and dungeon runs for Wyrmrest Accord. That said, don't neglect the 3 Wyrmrest dailies at Coldarra in Borean Tundra and the Wyrmrest Temple in Dragonblight.
For DPS, you'll probably want to go for Revered with the Ebon Blade for the head enchant, as well as the very nice DPS boots at exalted. Whether DPS or Tanking focused, getting the Sons of Hodir in Storm Peaks to at least honored for the shoulder enchants (or exalted for the better shoulder enchants) is a good thing to do for any non-inscriptionists, and DPSers will especially want to push to revered for a very nice pair of plate shoulders. You can start on that faction by the doing the They Took Our Men! quest, by the way.
And so on, and so forth
Of course, there's more you can do. Soloing Onyxia is one I've been meaning to tackle soon, and of course there's always AQ20 and Zul'Gurub, though those may take a bit of gearing up first. You can also pick an achievement tab and start working your way down. I'm doing that with fishing and cooking myself. There's a lot of stuff to be done, and no end in sight of it. It's a bright new expansion out there. Let's go exploring!